fix: don't point the image watcher at a remote session's directory

A remote-SSH session's workingDir is a path on the remote host, and the
image watcher watched it on the local disk: a folder that is not there,
or a same-named local folder whose images then popped up as the remote
session's. Same root cause as the Ralph @fix_plan.md watcher fix.

Three places start a watch, and all three now skip a remote session:
setupSessionListeners(), the app-wide toggle in PUT /api/settings (which
re-watches every enabled session), and POST /api/sessions/:id/image-watcher,
which refuses to turn it on (INVALID_INPUT, like the Git fetch settings
route) and still lets it be turned off. The Session Options row is hidden
for a remote session, the way the Git tab is, since the client's
_apiPost() does not throw on a refused request.

src/web/public/session-ui.js

@@ -2709,7 +2709,10 @@ Object.assign(CodemanApp.prototype, {
     // Git: the session's own choice if it has one, otherwise the app setting. updateGitFetchStatus is also
     // what SSE calls when a scheduled run lands, so the rows stay current while the modal is open.
     this.updateGitFetchStatus(sessionId);
-    document.getElementById('modalImageWatcherEnabled').checked = session.imageWatcherEnabled ?? true;
+    const imageWatcherToggle = document.getElementById('modalImageWatcherEnabled');
+    imageWatcherToggle.checked = session.imageWatcherEnabled ?? true;
+    // The server never watches a remote session's directory (it is on another host), so the row is hidden.
+    imageWatcherToggle.closest('.set-row').style.display = session.remote ? 'none' : '';
     document.getElementById('modalFlickerFilterEnabled').checked = session.flickerFilterEnabled ?? false;
 
     // Populate session name input with prefix/suffix split

src/web/routes/session-routes.ts

@@ -3780,6 +3780,11 @@ export function registerSessionRoutes(
     const { id } = req.params as { id: string };
     const body = parseBody(ImageWatcherSchema, req.body, 'Invalid request body');
     const session = findSessionOrFail(ctx, id, req);
+    // A remote session's workingDir is a path on the remote host; the watcher would watch it on the
+    // LOCAL disk (a missing folder, or a same-named local one whose images are not the session's).
+    if (body.enabled && session.remote) {
+      return createErrorResponse(ApiErrorCode.INVALID_INPUT, 'Image watching does not run for remote sessions');
+    }
 
     if (body.enabled) {
       imageWatcher.watchSession(session.id, session.workingDir);

src/web/routes/system-routes.ts

@@ -1183,9 +1183,10 @@ export function registerSystemRoutes(
 
       // Handle image watcher toggle dynamically
       toggleService((merged.imageWatcherEnabled as boolean) ?? false, imageWatcher, 'Image watcher', () => {
-        // Re-watch all active sessions that have image watcher enabled
+        // Re-watch all active sessions that have image watcher enabled (never a remote session: its
+        // workingDir is a path on the remote host, not on this disk)
         for (const session of ctx.sessions.values()) {
-          if (session.imageWatcherEnabled) {
+          if (session.imageWatcherEnabled && !session.remote) {
             imageWatcher.watchSession(session.id, session.workingDir);
           }
         }

src/web/server.ts

@@ -2067,8 +2067,10 @@ export class WebServer extends EventEmitter {
       session.ralphTracker.setWorkingDir(session.workingDir);
     }
 
-    // Start watching for new images in this session's working directory (if enabled globally and per-session)
-    if ((await this.isImageWatcherEnabled()) && session.imageWatcherEnabled) {
+    // Start watching for new images in this session's working directory (if enabled globally and per-session).
+    // A remote session's workingDir is a path on the remote host, and the watcher watches it on the LOCAL
+    // disk, so it is skipped there (the per-session and app-wide toggles skip it too).
+    if ((await this.isImageWatcherEnabled()) && session.imageWatcherEnabled && !session.remote) {
       imageWatcher.watchSession(session.id, session.workingDir);
     }